The present invention relates to a composition for metalizing ceramics, and more specifically to a composition of metal surface laid over low temperature-fired ceramics which is applicable to high density multi-layered wiring substrates, integrated circuits, transistor packages, and electrically insulated electronic parts.
A composition for metalizing low temperature-fired ceramics is fired simultaneously with the ceramics to form a metal surface thereon. Various compositions and conditions have been proposed for metalizing low temperature-fired ceramics. An example is disclosed in Japanese Published Unexamined Patent Application No. 63-295491, which varies the mixing ratio and grain size of CuO (copper(II) oxide) and Cu (copper) powdery mixture and adds TiO.sub.2 (titanium(IV) oxide), MnO.sub.2 (manganese(IV) oxide), Pt (platinum), Au (gold), or Ag.sub.2 O (silver(I) oxide) to the mixture to improve the conductivity, the hermeticity, and other properties of Cu-metalized layers.
A Cu-metalized layer is formed on ceramics through simultaneous firing of a Cu composition with the ceramics typically according to the following steps: (1) removing a binder in the atmosphere (binder removal step); (2) reducing CuO to Cu in H.sub.2 gas or decomposition gas (reduction firing step); (3) sintering and uniting ceramics and Cu in non-oxidation gas (final firing step).
The conventional method requires the above steps for depositing the metalized layer on ceramics and may thus have problems mentioned below.
In steps (1) and (2) of this process, unavoidable oxidation or reduction of copper powder results in variation of the total volume: increase by oxidation and decrease by reduction. The volume variation may cause uneven density in the metalized layer and generate honeycombed cracks 13 around the thinly layered region, and divide the layer into several blocks 12 as shown in FIG. 4. In such a case, the blocks 12 are not uniformly but locally sintered in the subsequent step (3) and worsen the conductivity or hermeticity of the metalized layer.
The mixing ratio of copper to copper oxide in the primary composition of the metalized layer is heightened for enhanced hermeticity. The higher copper ratio in the composition, however, causes large variation of volume due to oxidation of copper to copper oxide in the binder removal step (1), which results in burr of the metalized layer from the ceramic base.